<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        @keyframes rotateGradient {
            0% {
                transform: rotate(0deg);
            }

            100% {
                transform: rotate(360deg);
            }
        }

        .gradient {
            --size: 250px;
            --speed: 50s;
            --easing: cubic-bezier(0.8, 0.2, 0.2, 0.8);
            width: var(--size);
            height: var(--size);
            filter: blur(calc(var(--size) / 5));
            background-image: linear-gradient(rgba(55, 235, 169, 0.85), #5b37eb);
            animation: rotateGradient var(--speed) var(--easing) alternate infinite;
            border-radius: 30% 70% 70% 30%/30% 30% 70% 70%;
        }

        @media (min-width: 720px) {
            .gradient {
                --size: 500px;
            }
        }

        body {
            background-color: #222;
            position: absolute;
            inset: 0;
            display: flex;
            place-content: center;
            align-items: center;
            overflow: hidden;
        }

        /* This is just to transition when you change the viewport size. */
        * {
            transition: all 0.25s ease-out;
        }
    </style>
</head>

<body>
    <div class="gradient"></div>
</body>

</html>